The present invention relates generally to the field of magnetic data storage and retrieval systems. In particular, the present invention relates to a magnetic read head for use in a magnetic data retrieval system that has a magnetoresistive read sensor with side flux guides for providing longitudinal biasing to a sensing layer of the magnetoresistive read sensor.
A current-perpendicular-to-plane (CPP) magnetic read head is positioned over a magnetic disc or medium that is rotated at a high speed. The head is supported over a surface of the magnetic disc by a thin cushion of air produced by the high rotation speed. This surface is called an air bearing surface (ABS). The magnetic read head retrieves magnetically-encoded information that is stored on the disc. Several layers typically form the magnetic read head, including a top electrode, a bottom electrode, and a magnetoresistive (MR) read sensor positioned between the top and bottom electrodes. The electrodes may also function as shields to ensure that the read sensor reads only that information which is stored directly beneath it on the magnetic disc.
A time-dependent magnetic field from the disc causes modulation of a magnetization of the read sensor by rotating the sensor""s magnetization direction. Changes in the resistance of the read sensor can be detected by passing a sense current through the read sensor and measuring a voltage across the read sensor. A resulting signal is read by external circuitry to recover encoded information from the disc.
Biasing elements, or permanent magnets, made of a hard magnetic material are used to bias a sensing layer of the read sensor. The biasing elements are commonly arranged according to what is known in the industry as a standard abutted junction (ABJ), with the biasing elements arranged on opposing sides of the MR sensor, and with a pair of lateral isolation layers separating the respective biasing elements from the MR sensor. The MR sensor, isolation layers, and biasing elements are disposed collectively between the pair of electrodes.
The MR read sensor can be of any one of a number of giant magnetoresistive (GMR) read sensor types, including, but not limited to, a tunneling-giant magnetoresistive (TGMR) element, a spin valve (SV) element or a hybrid element. Both TGMR and SV elements have a ferromagnetic free layer and a ferromagnetic pinned layer. The free layer has a magnetic orientation capable of rotation, while the pinned layer has a magnetic orientation fixed in a predetermined direction, generally normal to the ABS. As is known in the art, the pinned layer generally has its magnetic orientation fixed by an exchange coupling with an antiferromagnetic layer placed upon the pinned layer. SV elements differ from TGMR elements in that a SV element has a conductive spacer layer located between the pinned layer and the free layer, while a TGMR element has an insulating or semiconducting barrier layer located between the pinned layer and the free layer. A hybrid GMR sensor may include a multilayer positioned between the free layer and pinned layer formed of a conductive spacer layer similar to the SV element and an insulating or semiconducting barrier layer similar to the TGMR element. Much of the general functioning of TGMR, SV, and hybrid GMR elements is similar. The magnetic orientation of the free layer is influenced by longitudinal biasing from the biasing elements, such that an easy axis of the free layer is generally set normal to the magnetization direction of the pinned layer. The longitudinal biasing of the free layer promotes both a substantially single-domain state and a reduction in noise in the free layer. The lateral isolation layers are used to adjust the magnitude of the longitudinal biasing applied to the free layer. This lateral isolation layer may be of a material having a high electrical resistivity, which also serves to reduce a diversion of some of the sense current into the biasing elements (known as shunting).
As magnetic storage and retrieval systems have developed greater capacities, greater areal bit densities have been employed. Smaller areal bit sizes have corresponded to the greater areal bit densities. Narrow reader widths are desired for retrieval of data stored on ultra-high density media having small areal size bits. More specifically, reader widths less than 0.1 xcexcm are desirable. These narrow reader widths seek to avoid off-track reading, where the read sensor simultaneously reads a plurality of adjacent bits which can thereby hinder data recovery. Previous configurations of CPP read heads, however, have not been able to provide proper longitudinal biasing as smaller CPP read heads are employed. As sensor widths have decreased, longitudinal biasing fields are sometimes too strong for the narrow MR sensors. Also, use of shape anisotropy, wherein a shape of a film tends to promote the formation of an easy axis in the film, becomes unavailing for establishing an easy axis in the free layer when reader widths are small.
Previous ABJ designs for reader widths less than 0.1 xcexcm have problems with a sensitivity loss due to a dead region at the junction region, a lack of shape anisotropy, a difficulty in consistently deploying lateral isolation layers, and a difficulty applying a proper magnitude of longitudinal biasing. As the size of the MR sensor decreases to keep up with greater areal densities of magnetic recording media, deviations in thicknesses of the lateral isolation layers make proper longitudinal biasing of small MR sensors problematic, where too much or too little flux can act upon the free layer of the MR sensor. Insufficient biasing can reduce the sensitivity of the MR sensor by failing to provide a substantially single-domain magnetic state along a width of the free layer of the MR sensor. Additionally, too much flux, or magnetic bias, provided by the longitudinal biasing elements may produce dead regions in the free layer where the magnetic orientation is unduly inhibited, effectively pinning the free layer. Extra flux may also produce multiple magnetic domains in the free layer. Dead regions and multiple magnetic domains in the free layer reduce the sensitivity of the MR sensor, hindering the retrieval of data from ultra-high density media. The sensor must also be stabilized against the formation of edge domains because domain wall motion results in electrical noise that makes data recovery impossible.
It has been important to maintain constant MR sensor output by increasing MR sensor sensitivity. In prior art designs, this goal has been accomplished by several methods, including decreasing a thickness of a sensing layer of the MR sensor and/or reducing a thickness of the permanent magnet bias elements and/or recessing the permanent magnet bias elements a distance from the MR sensor. However, previous configurations of MR sensors could provide too much or too little longitudinal bias to MR sensors having small reader widths used in conjunction with ultra-high density recording media, such as variations in the magnitude of longitudinal bias due to deviations in the thicknesses of the lateral isolation layers. This may produce asymmetrical biasing of a degree significant for small read sensor widths. When read sensor widths are less than about 0.1 xcexcm, previous designs present great difficulties in deploying longitudinal biasing while maintaining the narrow read sensor width. Process control issues arise as dimensions of CPP read sensor become small.
Longitudinal biasing can also be provided by biasing elements composed of a material having a high resistivity, such as oxide hard magnetic materials. A CPP reader having oxide biasing elements in a standard ABJ configuration can provide longitudinal biasing with little shunting of the sense current to the biasing elements. However, deploying the longitudinal biasing with such a design becomes problematic when the MR read sensor width becomes small and the proximity of the biasing elements produces undesirable extra flux.
The embodiments previously known in the art for providing longitudinal biasing have not addressed the problems encountered with MR read sensor widths below 0.1 xcexcm . Utilization of shape anisotropy to promote an easy axis in the free layer becomes problematic for MR reader widths below 0.1 xcexcm as a width of the free layer decreases with respect to a height of the free layer. Prior MR read sensor designs utilizing shape anisotropy had an easy axis of the free layer influenced by a free layer height to free layer width aspect ratio that relatively favored the reader width. As reader widths have shrunk in conjunction with smaller areal densities of media, the reader height to reader width aspect ratio no longer lends itself to establishing an easy axis in the free layer. Thus, longitudinal biasing is increasingly important, but reader widths below 0.1 xcexcm also present difficulties in deploying a proper magnitude of longitudinal biasing due to the dimensions of the read sensor upon which the biasing elements operate.
A novel design is needed to provide proper biasing to sensors for ultra-high density recording where sensor width is below 0.1 xcexcm while maintaining sensitivity in the sensor.
A transducing head according to the present invention includes a pair of electrodes, a pair of biasing elements and a magnetoresistive sensor. The magnetoresistive sensor is positioned between the pair of electrodes. The magnetoresistive sensor includes a pair of flux guides and a free layer positioned substantially co-planar with and between the pair of flux guides. The pair of electrodes are for providing a sense current to the free layer in a direction substantially perpendicular to a plane of the free layer. The pair of biasing elements are positioned on opposing sides of the magnetoresistive sensor for providing longitudinal bias to the free layer.